Cover interlock mechanism for a thermal printer locks cover while printing

Abstract: A cover interlock mechanism (12) for a thermal printer (10) is diclosed which locks the thermal printer cover when printing is being done and, when the print head (16) is in a disassembled position, unlocks the cover.

Description: BACKGROUND OF THE INVENTION Field of Invention The present invention relates to a thermal printer with a main support structure. Description of the Prior Art Thermal printers often provide a mechanism to replace the thermal dye donor media and/or the dye receiver media in the printer by opening a portion of the printer. To open the printer, the user releases a latch in a cover mechanism and swings the cover open to gain access to the media supplies. These cover mechanisms are usually located in the top portion of the printer, opening upward. The cover mechanism can have some of the major printer components attached to it, so that as the cover is swung open these components move away from media to permit easier loading of new media or for maintenance. The cover mechanism usually has a hinge or pivot axis along one side and a latch which keeps the cover closed during operation but permits opening the cover for loading media. To permit proper latch operation and opening, the cover cannot be rigidly locked to the rest of the thermal printer structure. The latch can usually be operated at any time, without regard to current printer operational status. Thus it is possible to open the cover mechanism when the printer is operating. Such situations can result in defective prints, operating problems requiring user intervention or even damaged equipment. US-A-5,198,836 shows for example a line thermal printer having a cover plate and a print head assembly. In the normal state during use of the printer the cover plate should be held in a closed position by a set of screws. However, the screws can be unscrewed and the cover plate can be opened at any time even during use of the printer, which can lead to the disadvantages of defective prints etc. as set forth above. SUMMARY OF THE INVENTION The object of the present invention is to eliminate defective prints, media jams and printer equipment damage caused by opening the cover mechanism when the printer is operating. This object is achieved in a thermal printer as set forth in claim 1 or 2. The printer may have a main support structure, comprising a cover mechanism, movable between open cover and closed cover positions, said cover mechanism including latching means with a first position for holding the cover mechanism in the closed cover position and a second position which permits said cover mechanism to be moved to the open cover position; a print head assembly movable between a print position and a retracted position; and an interlock mechanism responsive movement of said print head assembly said interlock mechanism locks said latching means to prevent moving said cover mechanism and releases said latching means to permit moving said cover mechanism. In the present invention, an interlock mechanism locks a latch mechanism in a closed position when a print head assembly is in a printing position, and the latch mechanism is unlocked when the print head assembly is in a retracted position, permitting opening of the cover mechanism. Advantages The following are the advantages of this invention: 1) a cover mechanism can be opened only when it will not interfere with printer operation; 2) a simple interlock mechanism of few parts which provides a solid mechanical lock for the cover mechanism, thereby preventing opening of the cover mechanism during printing; and 3) prevention of defective prints, media jams and printer equipment damage which may result from opening the cover mechanism during printer operation. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a sectional view of a thermal printer according to the present invention; FIG. 2 is an enlarged sectional view portraying FIG. 1's mechanism in more detail, showing the print head assembly, head positioning mechanism and cover mechanism in a print position; FIGS. 3A and B show a side and plan view, respectively, of a interlock mechanism in the print position, in which the interlock mechanism locks the latch in a closed position; FIG. 4 is an enlarged sectional view of FIG. 1's mechanism, similar to FIG. 2 except the print head assembly, head positioning mechanism and cover mechanism are in a retracted position; and FIG. 5 A and B show a side and plan view, respectively, of the interlock mechanism, similar to FIG. 3 except the interlock mechanism is in the released position, unlocking the latch to permit opening of the cover mechanism. DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described by referring to FIGS. 1 to 5. FIG. 1 shows a thermal printer 10 of the present invention wherein a cover mechanism 12 has several components attached to it. These components include a latch 14, a print head assembly 16 and dye donor supply spools 18. The cover mechanism 12 is mounted to a main support structure 20. When the latch 14 is released, the cover mechanism 12 can rotate to an open position. The main support structure 20 includes a roller platen assembly 22. The thermal printer 10 is shown as it operates, with the cover mechanism 12 in a closed position. During normal thermal printer operations, the print head assembly 16 can move to occupy at least two positions - (1) a printing position in which the print head assembly 16 is urged toward the platen 22, simultaneously pressing a dye donor and dye receiver and printing information thereon, and (2) a retracted position in which the print head assembly 16 is spaced away from the platen 22. The printer normally loads or ejects dye receiver media 24 with the print head assembly 16 in the retracted position. More than one retracted position can be used for the loading and ejecting phases of operation. During printing, the print head assembly is urged toward the platen, pressing the dye donor and dye receiver media between them. FIG. 2 shows the print head assembly 16 in the print position, a latch 14 in a closed position, and an interlock 36 in a locked position. The interlock 36 is pivotally mounted on a pivot pin 26. The interlock 36 further includes or defines a interlock engaging surface 28 on one end and a rod engaging surface 30 on the other end. An interface surface 32, shown in this embodiment as a pin, is attached to the print head assembly 16 is spaced away from the interlock engaging surface 28. It is recognized that alternative embodiments could utilize other features or components of the print head assembly for engaging the interlock engaging surface. The latch 14 can move side to side from a closed position to an open position. As the latch 14 moves, a locking rod 34 is urged from a closed position where the cover mechanism 12 is locked closed to an open position where the cover mechanism can be opened. When the interlock 36 is in the locked position, the rod engaging surface 30 restricts the motion of the locking rod 34 so that the locking rod 34 remains in its closed position. Resticting the locking rod 34 to its closed position further restricts the latch 14 to its closed position, thus locking the cover mechanism 12 in its closed position. FIGS. 3A and B shows a side and plan view respectively of the relative positions of the locking rod 34, the interlock 36 and the interlock surface 32 when the print head assembly 16 (not shown) is in its print position. When the printer has completed the printing operation, the print head assembly moves from the print position to the retracted position, permitting ejection of the finished print on the dye receiver media and subsequent loading of a new dye receiver media for the next print. FIG. 4 shows the print head assembly 16 in the retracted position, such as used for ejecting a finished print. When print head assembly 16 moves from the print position toward the retracted position, the interlock surface 32 contacts the interlock engaging surface 28. As the print head assembly continues its movement to the retracted position, the interlock surface 32 presses against the interlock engaging surface 28, causing the interlock 36 to rotate about the pivot pin 26. When the print head assembly 16 reaches the retracted position, the interlock 36 has rotated sufficiently such that the rod engaging surface 30 no longer restricts the movement of the locking rod 34. FIGS. 5A and B shows a side and plan view respectively of the relative positions of the locking rod 34, the interlock 36 and the interlock surface 32 when the print head assembly 16 (see FIG. 4) is in the retracted position. The interlock surface 32 presses against the interlock engaging surface 28, rotating the interlock 36 so that the rod engaging surface 30 no longer restricts the locking rod 34. When the print head assembly 16 is in the retracted position, the latch 14 can be moved from the closed to the open position because the locking rod 34 can now move freely from the locked position 40 to an unlocked position 42. The print head assembly 16 can also be moved to an intermediate retracted position between the printing and retracted positions shown in FIGS. 2 and 4. This intermediate retracted position can be used for loading a new dye receiver media. When the print head assembly 16 is in this intermediate retracted position, the locking rod engaging surface 32 of the interlock still restricts the movement of the locking rod, locking the cover mechanism in the closed position. Thus, the cover mechanism can be opened only when the print head is in the retracted position.

Claims: A thermal printer (10) with a main support structure (20) comprising: a) a cover mechanism (12); b) a print head assembly (16) movable between a print position and a retracted position; and c) an interlock mechanism responsive to the movement of said print head assembly (16). A thermal printer (10) with a main support structure (20) comprising: a) a rotatably mounted cover mechanism (12) movable between open cover and closed cover positions, said cover mechanism (12) including latching means with a first position for holding the cover mechanism (12) in the closed cover position during operation and a second position which permits the cover mechanism (12) to be moved to the open cover position at other times; b) a print head assembly (16) movable between a print position and a retracted position; and c) an interlock mechanism responsive to the position of said print head assembly (16) such that when said print head assembly (16) is in the print position, said interlock mechanism locks said latching means in the first position to prevent moving said cover mechanism (12) from the closed cover position, and further when said print head assembly (16) is in a retracted position, said interlock mechanism releases said latching means so that said latching means can move to the second position which thereby permits said cover mechanism (12) to be moved to the open cover position. A thermal printer (10) as set forth in claim 2, wherein said latch means includes: a) a latch (14) movable between closed and open positions; and b) a locking rod (34), movable between closed and open positions in response to the position of said latch (14), such that when said latch (14) is in its closed position said locking rod (34) is in its closed position, thereby locking said cover (12) in the closed cover position, and further when said latch (14) is in its open position, said locking rod (34) is in its open position, thereby unlocking said cover so that said cover can be moved to the open cover position. A thermal printer as set forth in claim 2 or 3, further including: a) defining said print head assembly (16) by an interlock surface; and b) said interlock mechanism further including a rotatably mounted interlock plate (36) defining a rod engaging surface (30) and an interlock engaging surface (28) whereby, when said print head assembly (16) is in the print position, said interlock surface (32) is spaced away from said interlock engaging surface (28) and said rod engaging surface (30) engages said locking rod (34), thereby restraining said locking rod (34) in its closed position; and further, when said print head assembly (16) is in the retracted position, said interlock surface (32) engages said interlock engaging surface (28), causing said interlock plate (36) to rotate until said rod engaging surface (30) disengages said locking rod (34) so it can move from its closed position to its open position, thereby permitting movement of said cover mechanism (12) to the cover open position.

Inventors: MINDLER ROBERT FREDRIC, WIRTH HENRY GEORGE, WIRTH, HENRY GEORGE, MINDLER ROBERT FREDRIC, EASTMAN KODAK COMPANY, WIRTH, HENRY GEORGE, EASTMAN KODAK COMPANY
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1994
Main classification: B41J29
IPC codes: B41J29, B41J25